WP 10894. Over the break we had 24hour CO2 tests with both annular and central masks to understand time constants effecting our circulating power transient alog 66548.
Attaching plots. CO2X Annular 4.7W, Central 3.0W. CO2Y Annular 4.2W, Central 3.3W.
Some interesting things:
- For the spherical power measured by HWS to stabilize with it take 30 minutes annular heat but >2hours with central heat!
- The LSRPWR_MTR measured power changes by ~1% over 2-3 hours after turn on. See plots. Dan Brown noticed this and suggested it could be caused by something on the CO2 table (maybe the masks) warming up. This effect would be too small to cause any IFO power up trnaiset we see.
- Plot attached comparaing these CO2 tests to ITM oplevs and L2 and M0 witness channels. You can see a small effect on the ITMs when the CO2s are turned on. ITMY L2 witness moves 1-2urad over the 24 test in the oposite way of the natural drift (pink and grey plots). ITMX L2 witness cannot be trusted at this time.
Elenna was questioning how long cool down takes. When the annular CO2 is turned off it takes 1 hour for spherical power to stabilize (right plot). Central CO2 is much slower, it takes >4 hours for spherical power to stabilize but it keeps drifting after this time. Plot attached.
There is a much longer time constant for the ITM surface curvature change. The CO2 laser heats the CP, th CP couples heat to the ITM and the HR surface becomes more curved. Modeling in COMSOL suggests that the 1/e time constant is about 2E4s. The attached images show (a) the configuration modeled in COMSOL - with 1W CO2 heat applied to the CP and (b) the change in the ITM ROC vs time after the CO2 laser is turned on at t=0s.
Configuration
Change in ROC vs time
Due to the linearity of the system, the cooldown will be the reverse of the above scenario.